Like I said, the logs will show in exactly the same place your Access and Threat Prevention logs will show, which is not /var/log/messages.
In my experience, the OS logs won’t appear to be very useful when viewed in SmartConsole/SmartView.
Possible they may be more useful if you write a parser for said logs, but we don’t provide one for that purpose by default.
If your goal is to collect the OS syslogs centrally, all devices should send their syslogs directly to your collector and not have them sent to your management.